1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a reflective and transflective liquid crystal display device, which has a storage capacitor, and its manufacturing method.
2. Description of the Related Art
In general, a liquid crystal display device is classified into two types, i.e., a transmissive liquid crystal display device using a back light as a light source and a reflective liquid crystal display device using not the back light but a natural light as the light source. The transmissive liquid crystal display device embodies luminous picture using the backlight as the light source even in a dark outside environment. However, the transmissive liquid crystal display device cannot use in a bright place and electricity is largely wasted.
On the other hand, the reflective liquid crystal display device, which does not use the backlight, can reduce largely the power consumption and its volume, thereby achieving a super thin type and lightweight type. However, there are limitations that the reflective liquid crystal display device cannot be used when the outside natural light is dim.
To overcome the above limitations, a transflective liquid crystal display device is disclosed. The transflective liquid crystal display device can be used as a reflective type or a transmissive type at need, as having both a reflection part and a transmission part inside unit pixel.
That is, the transflective liquid crystal display device is operated as the reflective liquid crystal display device by reflecting the outside light incident through a first substrate when the outside natural light is bright to an extent that the display function is capable without the back light. Moreover, when the outside light is not bright, the transflective liquid crystal display device is operated as the transmissive liquid crystal display device by irradiating the light of the back light to a liquid crystal layer through an opening part of a reflective electrode by using the back light.
Meanwhile, the liquid crystal display devices connect parallel a storage capacitor and a liquid crystal capacitor to assist the electric charge conservation capacity. The structure of the liquid crystal display devices is called a previous gate structure, as being formed between a gate and a pixel electrode.
The storage capacitor maintains voltage charged into the liquid crystal capacitor in a turn-off area of a corresponding thin film transistor. Therefore, in the turn-off area, the occurrence of leakage current can be prevented by the liquid crystal capacitor and the deterioration of picture due to the occurrence of flicker can be prevented.
Hereinafter, referring to the drawings, conventional reflective and transflective liquid crystal display device and its manufacturing method will be described.
FIG. 1a is a plan view of a conventional reflective liquid crystal display device and FIG. 1b is a sectional view of the reflective liquid crystal display device showing a cut surface along the line of I-I′ of FIG. 1a. FIG. 2a is a plan view of a conventional transflective liquid crystal display device and FIG. 2b is a sectional view of the transflective liquid crystal display device showing a cut surface along the line of II-II′ of FIG. 2a. 
In general, the liquid crystal display device includes a lower substrate called an aligning substrate of the thin film transistor, an upper substrate called a color filter substrate, and a liquid crystal layer formed between the two substrates. Hereinafter, the aligning substrate of the thin film transistor, which is the lower substrate, of the liquid crystal display device will be described.
First, as shown in FIGS. 1a and 1b, the lower substrate of the reflective liquid crystal display includes a data line 105 and a gate line 102, which are aligned on a substrate 101 in the form of a matrix to define the unit pixel, a thin film transistor having a gate electrode 102a formed at an intersection between the data line 105 and the gate line. 102, a gate insulation film 103, an semiconductor layer 104, source/drain electrodes 105a and 105b, a reflective electrode 107 electrically connected to the drain electrode 105b of the thin film transistor and occupying most of unit pixel area, and a storage capacitor having a capacitor lower electrode 102c and an capacitor upper electrode 105c electrically connected to the reflective electrode 107.
In detail, the gate line 102, the gate electrode 102a of the thin film transistor and the capacitor lower electrode 102c of the storage capacitor are formed by patterning simultaneously after depositing metal of low resistance by a sputtering method.
Furthermore, also the data line 105, the source/drain electrodes 105a and 105b of the thin film transistor and the capacitor upper electrode 105c of the storage capacitor are formed by patterning simultaneously after depositing conductive material of low resistance by the sputtering method.
At this time, on the entire surface of the substrate including the gate line 102, the gate electrode 102a and the capacitor lower electrode 102c is the gate insulation film 103 of silicone nitride (SiNx) film to insulate upper and lower layers, and an semiconductor layer 104 of an island form between the gate insulation film 103 and the source/drain electrodes 105a and 105b. On the entire surface of the substrate including the data line 105, the source/drain electrodes 105a and 105b and the capacitor upper electrode 105c is a passivation film 106 coated in a prescribed thickness.
The passivation film 106 has a pixel contact hole 108 of a prescribed depth and a capacitor contact hole 109 of a prescribed depth exposing a portion of the drain electrode 105b and a portion of the capacitor upper electrode 105c respectively. There is a reflective electrode 107 covering the contact holes at the unit pixel area on the passivation film. At this time, the reflective electrode has a depressed part in the contact hole.
The pixel contact hole 108 electrically connects the drain electrode 105b and the reflective electrode 107 and the capacitor contact hole 109 connects the reflective electrode 107 and the capacitor upper electrode 105c. 
The reflective electrode 107 is formed to occupy most of the unit pixel area constituted with only a reflection part(I) and made of metal having high reflectance, such as copper(Cu), chrome(Cr), Aluminum(Al), molybdenum(Mo), chrome/molybdenum(Cr/Mo) and chrome/aluminum(Cr/Al). The reflective electrode of the reflective liquid crystal display is important as being closely connected with brightness of picture. The transflective liquid crystal display further includes a transmission part(II) on the reflective liquid crystal display.
That is, as shown in FIGS. 2a and 2b, the transflective liquid crystal display includes a data line 205 and a gate line 202 aligned in the form of a matrix on a substrate 201, a thin film transistor formed on an intersection between the data line 205 and the gate line 202, a storage capacitor formed at a prescribed portion of the gate line, a first passivation film 206a formed on the thin film transistor and the storage capacitor, a reflective electrode 207a electrically connected with the thin film transistor and formed on the reflective part(I) of the unit pixel area, a second passivation film 206b formed on the entire surface including the reflective electrode 207a, and a transmissive electrode 207b formed on the transmission part(I) on the second passivation film 206b. 
At this time, the transmissive electrode 207b is made of ITO(Indium Tin Oxide), which is a transparent conductive material. The reflective electrode 207a is made of metal having a reflectance, such as copper(Cu), chrome(Cr), Aluminum(Al), molybdenum(Mo), chrome/molybdenum(Cr/Mo) and chrome/aluminum(Cr/Al), to reflect the outside light well. The transmissive electrode 207b and the reflective electrode 207a are connected with each other to form a pixel electrode 207.
In detail, the thin film transistor has a laminated film structure and includes a gate electrode 202a connected to the gate line 202, a gate insulation film 203, which is made of silicone nitride (SiNx), formed on the entire surface including the gate line 202, an semiconductor layer 204 made of amorphous silicone, and source/drain electrodes 205a and 205b connected to the data line 205. A reflective electrode 207a, which will be formed later, is electrically connected with the drain electrode through a pixel contact hole 208 formed by removing the first passivation film on the drain electrode 205b. As a result, a voltage according to the on-off action of the thin film transistor is applied to the reflective electrode 207a. 
The storage capacitor includes a capacitor lower electrode 202c, which is a portion of the gate line 202, an capacitor upper electrode 205c of an island form formed simultaneously with the data line 205, and a gate insulation film 203 interposed between the capacitor lower electrode 202c and the capacitor upper electrode 205c. The capacitor upper electrode 205c, which is formed in the island shape, is electrically connected with a pixel electrode 207 to impress voltage.
Such voltage impression is possible by connecting the pixel electrode 207 on the first passivation film 206a and the capacitor upper electrode 205c through a capacitor contact hole 209 formed by selectively removing the first passivation film 206a on the capacitor upper electrode 205c. At this time, the pixel electrode, i.e., the reflective electrode formed in the capacitor contact hole has a depressed part corresponding to a depth of the capacitor contact hole.
The transflective liquid crystal display constructed as the above transmits voltage impressed on the pixel electrode 207 through the drain electrode 205b to the capacitor upper electrode 205c connected through the capacitor contact hole 209, thereby forming capacitance between the upper and capacitor lower electrodes 205c and 202c. 
However, the conventional reflective and transflective liquid crystal display device and its manufacturing method have the following problems.
In case of forming the storage capacitor of the reflective and transflective liquid crystal display, when the capacitor upper electrode and the pixel electrode on the passivation film are connected with each other through the capacitor contact hole formed by removing the passivation film, a portion of the pixel electrode is depressed by the contact hole, and the retardation because of a cell gap difference by the depressed portion is increased more than a design value, thereby lowering an optical efficiency.
Particularly, if a thick passivation film is used to enlarge the cell gap of the transmission part of the transflective liquid crystal display, the capacitor contact hole is depressed more, thereby lowering the optical efficiency more.